beta-Peptide Conjugates: Syntheses and CD and NMR Investigations of beta/alpha-Chimeric Peptides, of a DPA-beta-Decapeptide, and of a PEGylated beta-Heptapeptide

beta(3)-Peptides consisting of six, seven, and ten homologated proteinogenic amino acid residues have been attached to an alpha-heptapeptide (all D-amino acid residues: 4), to a hexaethylene glycol chain (PEGylation; 5c), and to dipicolinic acid (DPA derivative 6), respectively. The conjugation of the beta-peptides with the second component was carried out through the N-termini in all three cases. According to NMR analysis (CD3OH solutions), the (M)-3(14)-helical structure of the beta-peptidic segments was unscathed in all three chimeric compounds (Figs. 2, 4, and 5). The alpha-peptidic section of the alpha/beta-peptide was unstructured, and so was the oligoethylene glycol chain in the PEGylated compound. Thus, neither does the appendage influence the beta-peptidic secondary structure, nor does the latter cause any order in the attached oligomers to be observed by this method of analysis. A similar conclusion may be drawn from CD spectra (Figs. 1, 3, and 5). These results bode well for the development of delivery systems involving beta-peptides.